1. Field of the Invention
This invention is directed to methods and apparatus for identifying regions of interest in medical imaging data, particularly in imaging data represented in an intensity projection image, such as an MIP (Maximum Intensity Projection).
2. Description of the Prior Art
In the medical imaging field, several imaging schemes are known. For example PET (Positron Emission Tomography) is a method for imaging a subject in 3D using an injected radio-active substance which is processed in the body, typically resulting in an image indicating one or more biological functions. Other such functional imaging modalities are known, such as SPECT.
In such functional images, many important pathologies and anatomical structures appear as very high (or low) intensities. For example, a tumor in an FDG-PET image will often appear as a bright region or “hotspot”.
A Maximum Intensity Projection (MIP) image is a useful way to visualize such medical images. Each pixel in a MIP is the maximal intensity along a ray orthogonal to the plane of the MIP. The resulting pixel values come from different depths along the rays and hence a MIP can be thought of as a simple form of 3D visualization.
In oncology, the rotating maximum intensity projection (MIP) is typically the first image reviewed by a PET reading physician to provide a quick overview of the case. The MIP allows rapid localization of potential lesions and can be used to navigate to regions of interest in the multi planar reconstruction views.
Due to the nature of the MIP, a hotspot will only be visualized if it contains the highest voxel value along one of the lines of projection (rays) used to generate the MIP (FIG. 1). Furthermore, it will only be identifiable on the MIP if it is also a hotspot (or local maximum) on at least one of the 2D MIP images.
In the example shown in FIG. 1, an axial image slice 100 from medical image data of a subject, the hotspot 102 would not be visualized on any of the MIP angles 106 if the uptake in the liver 104 was higher than that in the hotspot. This is because each of the rays to construct the 2D MIP at any of the angles (106) contains a higher maximum voxel (in the liver) than the hotspot. It is therefore possible that clear hotpots in the image volume will not be visualized on the MIP.
Typically in current clinical reads, the MIP is generally used to give an initial overview of the case, but relies on a detailed review of the MPRs to fully read the case, as providing the MPR read is thoroughly, any MIP-hidden hotspots could still be read on the MPR. This of course requires further steps, time and costs.
In addition, although MIP-hidden hotspots may be visible in the MPRs, any MIP-based features for interacting with the MPRs will not be available; for example, clicking on the hotspot in the MIP to center the crosshairs in the MPR, or clicking on the hotspot in the MIP to segment it.